1. Field of the Invention
The present invention relates to a gene implicated in abiotic stress tolerance and growth promotion and a method for improving abiotic stress tolerance and promoting growing of transformed plants with the same.
2. Description of the Related Art
Due to their sessile nature, higher plants are constantly faced with various adverse environmental factors, including drought, high salt, heavy metals, cold, heat shock, and ozone, during their whole life span. These abiotic stresses are a limiting factor for the growth and development of crop plants. Water deficiency causes dramatic reduction of crop production globally, and the decreasing availability of fresh water may pose a future threat to humans and higher plants. Plants have diverse defense strategies to enhance their tolerance to transient and long-term water shortages by triggering signaling network pathways and inducing stress-responsive genes. The cellular and genetic defense mechanisms in response to water stress have been widely documented (Shinozaki and Yamaguchi-Shinozaki, 2007). However, for stress tolerance or sensitivity, our knowledge concerning the biological functions of stress-related genes in higher plants is still rudimentary. Therefore, it is important to study the functions of stress responsive genes to increase the productivity and distribution of crop plants.
Ubiquitin is a protein consisting of 76 amino acids and it has been found in almost all tissues of eukaryotic organisms. Ubiquitin has a characteristic that is covalently bound to various substrate proteins by E1-E2-E3 consecutive actions of ubiquitin-activating enzymes (E1s), ubiquitin-conjugating enzymes (E2s) and ubiquitin ligases (E3s). The substrate proteins to be attached with ubiquitin are very diverse, affecting almost all physiological activities. In addition, many studies have been found that the many diseases are associated with these mechanisms. A function of ubiquitin is firstly known to promote degradation of protein by attaching with other proteins. However, other functions of ubiquitin have been recently revealed one after another.
Ubiquitin is attached to substrate by consecutive actions of three types of proteins, i.e., E1, E2 and E3. The glycine residue at the C-terminal domain of ubiquitin binds to NH3 at R— group of lysine residues on the substrate protein, thereby forming a covalent bond with the substrate. In general, proteins attached with ubiquitin are degraded by proteasome. Polyubiquitin as a chain of several ubiquitin molecules has to be attached to the substrate for degradation by proteasome. Until now, it has been known that proteasome-dependent degradation of the substrate occurs only when polyubiquitin consisting of at least four ubiquitins is attached to the substrate; however, it would be controversial since these results were obtained from in vitro experiments. Polyubiquitination leading to the proteasome-dependent degradation is the linkage form in which the 48th lysine residue of one ubiquitin is linked to another ubiquitin.
There are 2 types of E1 enzymes in organism. There are various types of E2s. In general, E2s catalyse the transfer of ubiquitin from E1 to E3 or substrate. E3s which are also known as E3 ligases catalyse the final step of the ubiquitination cascade. E3s determine specificity of the substrate to be ubiquitinated. In other words, the substrate being capable of interaction with certain E3s is specifically determined. E3 enzymes may be classified into two major types according to domains. E3 enzymes possess one of two domains: the homologous to the E6-AP carboxyl terminus (HECT) domain and the really interesting new gene (RING) domain. E3 enzymes having RING domain serves to position E2 and substrate in close proximity each other. In other words, where E2 and the substrate bind to E3, distance between ubiquitin of E2 and the substrate is formed to close sufficiently such that ubiquitin of E2 is chemically passed to the substrate. In contrast, E3 enzymes having HECT domain receive ubiquitin from E2, and then transfer it to the substrate. The At5g01520 gene codes for the protein having E3 ubiquitin ligase enzymatic activity. The ubiquitination has been known to serve diverse functions as one of the mechanism that all higher organisms as well as plants have. However, the genes involved in abiotic stresses have been unknown. The present inventors have isolated the At5g01520 genes in which the expression is induced by abiotic stresses and ABA hormone in Arabidopsis thaliana. Then, they have prepared At5g015265-overexpresors and knock-out mutants and analyzed their physiological phenotypes.
Throughout this application, various publications and patents are referred and citations are provided in parentheses. The disclosures of these publications and patents in their entities are hereby incorporated by references into this application in order to fully describe this invention and the state of the art to which this invention pertains.